Epithelia are continuously regenerating structures and there is some evidence that a continuous influence of the subepithelial connective tissue is required to maintain the regional specificity of epithelial structure. Oral mocosa shows a marked regional variation in structure and such variation appears to be related in regional differences in function. Many pathological processes in the oral cavity are associated with changes in the maintenance of epithelium. Epithelial maintenance can be considered in relation to control of three types of cellular activity: rates of synthesis, types of synthesis and establishment of tissue architecture. The objectives of the proposed research are to evaluate whether, a) different stratified squamous epithelia have the same basic pattern of differentiation, b) there is a regional specificity of subepithelial connective tissue, which continuously modulates structure, c) epithelia are capable of remodulation, d) the rate and type of epithelial synthesis occurring are independently controlled and e) a specific connective tissue cell type can be identified as responsible for maintaining epithelial specificity. These problems will be investigated by examing homotypically and heterotypically recombined epithelial and connective tissues grown in protected sites in histocompatible mice.